serial: Refactor uart_flush_buffer() from uart_close()

In the context of the final tty & port close, flushing the tx
ring buffer after the hardware has already been shutdown and
the ring buffer freed is neither required nor desirable.

uart_flush_buffer() performs 3 operations:
1. Resets tx ring buffer indices, but the tx ring buffer has
   already been freed and the indices are reset if the port is
   re-opened.
2. Calls uart driver's flush_buffer() method
   5 in-tree uart drivers define flush_buffer() methods:
     amba-pl011, atmel-serial, imx, serial-tegra, timbuart
   These have been refactored into the shutdown() method, if
   required.
3. Kicks the ldisc for more writing, but this is undesirable.
   The file handle is being released; any waiting writer will
   will be kicked out by tty_release() with a warning. Further,
   the N_TTY ldisc may generate SIGIO for a file handle which
   is no longer valid.

Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

5 files changed, 34 insertions, 28 deletions

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 02016fcd91b8..8469b66ff832 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1689,6 +1689,7 @@ static void pl011_shutdown(struct uart_port *port)
                         plat->exit();
         }
 
+        pl011_dma_flush_buffer(port);
 }
 
 static void
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index edde3eca055d..8a84034d130c 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1802,6 +1802,20 @@ free_irq:
 }
 
 /*
+ * Flush any TX data submitted for DMA. Called when the TX circular
+ * buffer is reset.
+ */
+static void atmel_flush_buffer(struct uart_port *port)
+{
+        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
+
+        if (atmel_use_pdc_tx(port)) {
+                UART_PUT_TCR(port, 0);
+                atmel_port->pdc_tx.ofs = 0;
+        }
+}
+
+/*
  * Disable the port
  */
 static void atmel_shutdown(struct uart_port *port)
@@ -1852,20 +1866,8 @@ static void atmel_shutdown(struct uart_port *port)
         atmel_free_gpio_irq(port);
 
         atmel_port->ms_irq_enabled = false;
-}
 
-/*
- * Flush any TX data submitted for DMA. Called when the TX circular
- * buffer is reset.
- */
-static void atmel_flush_buffer(struct uart_port *port)
-{
-        struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
-
-        if (atmel_use_pdc_tx(port)) {
-                UART_PUT_TCR(port, 0);
-                atmel_port->pdc_tx.ofs = 0;
-        }
+        atmel_flush_buffer(port);
 }
 
 /*
diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
index 53d7c31ce098..78a5cf65bf02 100644
--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -1034,6 +1034,20 @@ fail_rx_dma:
         return ret;
 }
 
+/*
+ * Flush any TX data submitted for DMA and PIO. Called when the
+ * TX circular buffer is reset.
+ */
+static void tegra_uart_flush_buffer(struct uart_port *u)
+{
+        struct tegra_uart_port *tup = to_tegra_uport(u);
+
+        tup->tx_bytes = 0;
+        if (tup->tx_dma_chan)
+                dmaengine_terminate_all(tup->tx_dma_chan);
+        return;
+}
+
 static void tegra_uart_shutdown(struct uart_port *u)
 {
         struct tegra_uart_port *tup = to_tegra_uport(u);
@@ -1046,6 +1060,8 @@ static void tegra_uart_shutdown(struct uart_port *u)
         tegra_uart_dma_channel_free(tup, true);
         tegra_uart_dma_channel_free(tup, false);
         free_irq(u->irq, tup);
+
+        tegra_uart_flush_buffer(u);
 }
 
 static void tegra_uart_enable_ms(struct uart_port *u)
@@ -1174,20 +1190,6 @@ static void tegra_uart_set_termios(struct uart_port *u,
         return;
 }
 
-/*
- * Flush any TX data submitted for DMA and PIO. Called when the
- * TX circular buffer is reset.
- */
-static void tegra_uart_flush_buffer(struct uart_port *u)
-{
-        struct tegra_uart_port *tup = to_tegra_uport(u);
-
-        tup->tx_bytes = 0;
-        if (tup->tx_dma_chan)
-                dmaengine_terminate_all(tup->tx_dma_chan);
-        return;
-}
-
 static const char *tegra_uart_type(struct uart_port *u)
 {
         return TEGRA_UART_TYPE;
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 1166c52e51f4..787d67f74bd9 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1361,7 +1361,6 @@ static void uart_close(struct tty_struct *tty, struct file *filp)
 
         mutex_lock(&port->mutex);
         uart_shutdown(tty, state);
-        uart_flush_buffer(tty);
 
         tty_ldisc_flush(tty);
 
diff --git a/drivers/tty/serial/timbuart.c b/drivers/tty/serial/timbuart.c
index 0d11d5032b93..e9e252324fb6 100644
--- a/drivers/tty/serial/timbuart.c
+++ b/drivers/tty/serial/timbuart.c
@@ -273,6 +273,8 @@ static void timbuart_shutdown(struct uart_port *port)
         dev_dbg(port->dev, "%s\n", __func__);
         free_irq(port->irq, uart);
         iowrite32(0, port->membase + TIMBUART_IER);
+
+        timbuart_flush_buffer(port);
 }
 
 static int get_bindex(int baud)